> Filesystems like ext2 put their superblock 1 block into the partition> in order to avoid overwriting disk labels and other uglies. UFS does> this too, as do several others. One of the few exceptions I've been> able to find is XFS.> > This is a real issue on sparc where the default sun disk labels> created use an initial partition where block zero aliases the disk> label. It took me a few iterations before I figured out why every> btrfs make would zero out my disk label :-/

Actually it seems this is only a problem with mkfs.btrfs, it clearsout the first 64 4K chunks of the disk for whatever reason.